The present invention relates to a sheet feeder device for feeding document sheets, an image reading apparatus and an image forming apparatus.
Recently, efficient image reading or image forming has become possible by setting, on an image forming apparatus for example, a document reading apparatus configured to automatically feed documents in the form of sheets for successive reading. Further, with increasing speed in reading an image of a document, converting the image into electronic data and forming an image based on the electronic data by virtue of the development of digital technology, it has become possible to process a larger number of document sheets at high speed. Such a recent document reading apparatus allows a very large number of document sheets, for example about 100 to 200 sheets, to be set thereon at a time. Further, the improvement of the document feeder section of the document reading apparatus has made it possible to feed various types of document sheets.
The above-described image reading apparatus, which is configured to feed a number of sheets such as document sheets set thereon and read images formed on the sheets, picks up the document sheets stacked on a document tray one by one for image reading. To feed only a single sheet of the document stack to a reading section, use is made of a separating mechanism comprising a combination of a feed roller and a reverse roller. Specifically, when plural sheets are picked up at a time, the lower sheet(s) contacting the reverse roller is returned to the document tray so that only the sheet contacting the feed roller can be fed to a feed path leading to the reading section.
In such an arrangement, the reverse roller of the separating mechanism is connected, via a torque limiter, to a driving section for rotating the reverse roller in a direction opposite to the rotating direction of the feed roller. At a load torque working when only a single document sheet is pinched by the separating mechanism, the reverse roller slips relative to the driving section and hence rotates in the direction of movement of the document sheet, thereby allowing the sheet to pass through the separating mechanism. On the other hand, when two or more sheets are to be pinched, the load torque increases and the torque limiter prevents the reverse roller from slipping, so that the reverse roller rotates in the direction opposite to the sheet feed direction. As a result, only a single sheet is allowed to pass through the separating mechanism reliably.
Generally, the feed roller confronting the reverse roller and the pick-up roller for paying out sheets are each supported on the apparatus body in a cantilevered fashion so that they can be replaced easily at the time of maintenance or in the case where the function for preventing sheets from being fed as superposed on each other is deteriorated due to friction or the like or any other trouble occurs. (See paragraphs 0023-0025 and FIGS. 1 and 2 of Japanese Patent Laid-Open Publication No. 2002-60066, and paragraphs 0008-0013 and FIG. 4 of Japanese Patent Laid-Open Publication No. HEI 6-144607, for example.)
However, for the reasons that the reverse roller contacting the feed roller is generally disposed under the feed roller and the feed roller is supported in a cantilevered fashion, when the reverse roller confronting the feed roller is also supported in a cantilevered fashion as in the aforementioned Japanese Patent Laid-Open Publications No. 2002-60066 and No. HEI 6-144607, the two rollers cannot be held in contact with each other stably, which likely results in lowered sheet separating performance.
When the sheet separating performance is lowered, problems such as feeding of sheets as superposed on each other or a jam are likely to occur. For this reason, it is a general practice to support the reverse roller at both ends thereof. However, such a both ends support structure makes attachment or detachment of the roller difficult, thus rendering the maintenance troublesome.